I am trying to get some help in sizing my exhaust pipe for my 1997 Pontiac Trans Am WS-6

Can anybody point me in the right direction for equations?

I pulled out my Marks handbook hoping it would help, but I couldnt find anything

Currently, I have long tube headers with a 1.75 inch primaries 3 inch collectors then going into a 2.5 inch y-pipe that has 3 inch cut-outs which then has regular catalytic converters then into a 3" Flowmaster catback.

I want to redo the y-pipe because it was cheaply made (in college)
I eventually want to go to a true dual exhaust system.

>>>>>>>>>>>>>>>>needle valve

Hello, there is a plethora of aftermarket for your application. It would seem a little overkill to try and calculate with any certainty the size of the primaries for your car. The aftermarket companies (at least the good ones) have already done this for you; just buy a set of headers and you'll be fine especially for a street WS6 with stock displacement motor.

Now if you intend to build a motor that revs higher, has larger/smaller displacement and uses custom ported heads/valvejob than you may need to look into getting with a custom cam designer and tune your header length to that.

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